We recently wrote about the positive effect of magnesium supplementation on blood pressure. "Magnesium is not the only supplement that lowers blood pressure," wrote a reader after reading that post. "My blood pressure went down considerably after I took vitamin C." A meta-study published in 2012 in the American Journal of Clinical Nutrition suggests that this is not impossible.

Study
The authors of the meta-study gathered 29 studies in which the subjects had taken vitamin C and the researchers had measured the effect of the supplementation on the subjects' blood pressure. The average dose taken was half a gram of vitamin C per day, and the average length of supplementation was two months.

Now a reduction of 4 points in the systolic pressure and 1.5 points in the diastolic pressure might not be much, but the researchers discovered that the blood pressure-lowering effect of vitamin C seemed to increase in combination with other interventions. We are cautious in our formulation, because the correlations suggested in the figure below are not statistically significant.

Moreover, the effect of the vitamin C seemed to increase the longer the subjects took their supplements, as you can see in the figure above. But the effect of the length of use was not statistically significant either.

Conclusion
"Our meta-analysis suggests that vitamin C supplementation may have a useful role in lowering blood pressure", the researchers write. "However, before vitamin C supplementation can be recommended for the prevention of hypertension or as adjuvant antihypertensive therapy, additional trials are needed, designed with large sample sizes, and with attention to quality of blood pressure assessment."